The goal of the proposed research is to gain a better understanding of the molecular basis of asexual reproduction and development in the pea aphid, Acyrthosiphon pisum. Asexual reproduction in aphids occurs in response to specific environmental cues, allowing this insect to rapidly colonize a host plant in clonal fashion during the spring and summer months. This switch to asexual reproduction requires not only the perception of environmental cues, but also a suite of changes in both meiosis and embryonic development. The goal of this project is to identify molecules that are specifically involved in this process and thereby cast light on the mechanism of asexuality. The specific aims are (1) to perform a genetic screen for mutants that, while able to reproduce and develop sexually, fail to do so asexually, (2) to map and clone loci responsible for isolated mutants using an already established genomic BAC library, as well as a microsatellite-based linkage map currently under construction, (3) to clone aphid orthologs of genes known from Drosophila to play a role in the regulation of female meiosis I and investigate their expression in both sexual and asexual germaria, and (4) to use RNA interference to block the expression of candidate genes in sexual germaria by injection into sexual females and by developing an in vitro culture system for aphid ovarioles.